WA once had its own species of koala. Then the forests collapsed

An illustrative reconstruction of the WA koala Phascolarctos sulcomaxilliaris which is thought to have gone extinct several thousand years ago. (WA Museum: Nellie Pease) Distinct grooves, or dimples, in the cheekbones of koala skulls found in Western Australia have helped identify a new species of extinct koala. The WA or dimpled koala (Phascolarctos sulcomaxilliaris) lived in eucalypt forests until a major climate event wiped out their habitat about 28,000 years ago. It's the only species of koala known to have lived in WA besides east coast specimens introduced in the past 90 years to a Perth conservation reserve and wildlife parks. Link copiedShareShare articleAustralia's west coast had its own species of koala until about 28,000 years ago when eucalypt forests collapsed. The newly described extinct species, Phascolarctos sulcomaxilliaris, was named following the analysis of two skulls donated to the WA Museum Boola Bardip. Kenny Travouillon, the museum's mammals curator, said the more you compared the skulls with modern koalas (Phascolarctos Cinereus), the more differences there were. "The one feature that really made it obvious [it was a different species] was there was big grooves in the cheeks of the skull, like dimples," Dr Travouillon said. "And none of the skulls in the modern collection had these dimples in the cheekbones." Instructions: Use left and right arrow keys to control image transition SLIDE Left: A skull from a regular koala (Phascolarctos cinereus) / Right: A skull from a WA koala (Phascolarctos sulcomaxilliaris). (Royal Society Open Science: WA Museum)Those bone dimples may have allowed the new species, nicknamed the WA or dimpled koala, to have more muscles in its face. Dr Travouillon and his co-authors suggested in a new study, published today in Royal Society Open Science, this might have meant the dimpled koala had larger lips or the ability to flare its nostrils to help detect food. The authors also re-examined koala bones previously collected in WA and concluded they all belonged to this new species. This means there is no record of the modern koala ever living on the west coast, outside of more recently introduced specimens to Yanchep National Park and wildlife parks. Modern koalas have lived in Yanchep National Park, in the north of Perth, since a colony was established in 1938. (ABC Radio Perth: Emma Wynne) The skulls, donated by the late Margaret River caver Lindsay Hatcher and his family, provide insights into eating ability and brain size. While the dimpled koala would have been a similar size to modern koalas, there were several differences in their anatomy. WA Museum mammals curator Kenny Travouillon being lowered into a cave to hunt for fossils. (Supplied: WA Museum) Dr Travouillon said the dimpled koala may have had even less brain power than its east-coast cousin, which has one of the smallest brain-to-body ratios among mammals. "In modern koalas there's an elongation of the back of the brain case, which this species doesn't have," he said. "Koalas are not famous for being smart, but these ones probably were not as smart again." The dimpled koala might have also spent less time chewing its food, presumably eucalyptus leaves, than the modern species. That's because of wider teeth and a different angle to its jaw enabling more efficient chewing. The skull and lower jaw of a female dimpled koala (Phascolarctos sulcomaxilliaris). (Royal Society Open Science: WA Museum) Their bones were also thinner than modern koalas, Dr Travouillon said, suggesting the dimpled koala had smaller muscles and was possibly less agile. "So they spent less time moving between trees and stayed put as much as possible," he said. University of New South Wales palaeontologist Tim Churchill, who was not involved in the study, said the skull of the dimpled koala looked more robust than modern species. "In combination with several distinct dental features and those bizarre concave sulci [cheek grooves] … it's definitely a different animal," he said. Dr Churchill said there was a lot of possibilities for what the dimples meant in terms of the extinct koala's biology. He suggested it could be the dimpled koala had a greater reliance on smell than sound. "It's interesting to find such a distinctive feature with taxonomic merit but also as another interesting aspect of biology that we're scratching our heads about." Modern koalas are the last of a genus of animals known as Phascolarctos, which emerged about five million years ago in the late Miocene or early Pliocene. The number of species in the genus is disputed but is thought to be about four including dimpled and modern koalas. Australia was starting to dry and forests were retreating in the time that WA's dimpled koalas emerged, which could explain how the animals became geographically separated from the rest of their genus. But Dr Travouillon said it was hard to know when the connection between the species was seve

WA once had its own species of koala. Then the forests collapsed

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